1. Field
This invention relates generally to internal combustion engines and more particularly to an improved scavenging method and means for substantially increasing the power of two cycle internal combustion engine.
2. Prior Art
As is well known to those versed in the internal combustion engine art, a two cycle internal combustion engine has a piston which undergoes alternate compression and power strokes, and a combined intake-exhaust phase during a terminal portion of each power stroke and an initial portion of the following compression stroke of the piston. During this intake-exhaust phase, the piston uncovers intake and exhaust ports in the cylinder wall to exhaust spent combustion gas from the cylinder through the exhaust port or ports and admit air/fuel mixture, hereafter referred to simply as fuel mixture, to the cylinder through the intake port or ports. During each piston compression stroke, a partial vacuum is created in the engine crankcase chamber which induces intake air flow through the engine carburetor into the chamber to provide a charge of fuel mixture in the chamber. This fuel mixture is compressed in the chamber during the following piston power stroke and then displaced into the engine cylinder through the cylinder intake ports during the next intake-exhaust phase of the engine.
Two cycle engine operation presents one problem to which this invention is addressed. The problem referred to involves scavenging of spent combustion gas from the cylinder and charging of the cylinder with fuel mixture during each intake-exhaust phase of the engine. Thus, in a two cycle engine, exhaustion of the spent combustion gas and admission of the fuel mixture occur essentially simultaneously, except of course that exhausting of the spent gas commences slightly before admission of the fuel mixture due to initial uncovering of the exhaust ports by the piston slightly before the intake ports. The spent combustion gas is scavenged from the cylinder by the incoming fuel mixture rather than by positive displacement as in a four cycle engine. Since the volume of spent gas remaining in the cylinder at the end of each intake-exhaust phase detracts from the power developed by the engine, efficient scavenging of the spent gas during each intake-exhaust phase is essential to satisfactory engine operation.
A variety of two cycle engine designs have been developed in an attempt to improve this spent gas scavenging action and thereby increase engine power. Two of these engine designs, which are the most widely used, are commonly referred to as Schnierly-ported and baffled piston types. The Schnierly-ported engine relies on a unique arrangement of the cylinder intake and exhaust ports to accomplish efficient scavenging. The baffled piston engine relies on a projecting baffle on the piston, between diametrically opposed intake and exhaust ports, to accomplish efficient scavenging. This baffle deflects the incoming fuel mixture during each intake-exhaust phase of the engine toward the cylinder head to scavenge spent gas from the cylinder head region.
The present invention provides improvements in this latter baffled piston type engine which cure a deficiency inherent in this type of engine. This deficiency resides in the fact that deflection of the incoming fuel mixture by the piston baffle creates in the region behind the baffle relative to the cylinder intake ports, that is the region at the side of the baffle opposite the intake ports, a relatively dead zone from which spent combustion gas is not scavenged. The spent gas remaining in this region at the end of each intake-exhaust phase of the engine represents a substantial loss of potential engine power. That is to say, if this region contained fuel mixture rather than spent gas, the total volume of mixture in the cylinder at ignition, and hence the engine power, would be substantially increased. Thus improved at reasonable cost, the baffled piston engine would be superior to the Schnierly-ported engine because of the relatively high cost of the latter engine.